Electronic components, such as integrated circuits (ICs), may include one or more electronic circuits (e.g., a chip or “die”). These circuits may be encased in a package and possibly arranged on a die pad. The package may include a plastics or ceramic packaging (e.g., a molding compound or MC) with die pads coupled to pins of the package, with the die sealed within the package and electrically conductive wires (e.g., gold) coupling the pads to the pins.
Such wires were once attached by hand. In present-day technology that task is performed by machines, leading to a lead frame (LF), which is a set of metal leads that extend outside the package/housing to form electrical connection pins for the component.
Lead frames may be produced with a variety of processes. For instance, lead frames may be etched e.g. by photolithographic processes, by using light to transfer a geometric pattern from a photo-mask onto a light-sensitive, chemical “photoresist” layer deposited on a metallic strip. Once developed, the resist layer may be chemically removed from all those areas not affected by the exposure pattern and a photo mask remains on the metal surface to protect locally the strip from the etching action of e.g., an acid flow.
Lead frames may also be stamped by creating a frame design on a strip by the progressive action of plural punches that remove material from the strip by mechanical action.
Producing a routing to allow dedicated pin-out starting from an existing device is difficult with any of those processes.
Such standard technologies do not easily permit leads to be crossed and electrically insulated. Any “signal crossing” may then be managed through wire bonding (which may result in an increase of wire length, wire sweeping and/or reduced wire distance).
Also, the pad layout of the semiconductor (e.g., silicon) may be linked to lead frame design and creating downsets may involve plastic deformation obtained with dedicated tooling.
Production technologies based on material removal (chemical/mechanical) thus impose limitations on lead frame design.
Possible drawbacks of conventional processes for producing lead frames based on chemical/mechanical removal of material may include one or more of the following:
reduced lead frame design flexibility may not permit to adapt the lead configuration to a die with a constrained pad layout;
a device pad layout may be dictated by the desired pad out of the final product and thus require to be customized on that basis;
an existing device may be hardly compatible with different package types, e.g., a die for dual-in-line packages may not be compatible with a single-in-line package;
a dedicated tool may be involved in plastic deformation for each downset of the frame (tie bar, ground ring, power bar);
managing thickness variations in different frame areas may involve milling of a coil with limited design configuration; and
controlled and increased lead frame finishing (surface roughness) almost inevitably involves electro plating or etching, selective plating/etching managed through masking.